Saved by another's faith?

3:1 Then the word of the LORD came to Jonah the second time, saying,
3:2 "Arise, go to Nin'eveh, that great city, and proclaim to it the message that I tell you."
3:3 So Jonah arose and went to Nin'eveh, according to the word of the LORD. Now Nin'eveh was an exceedingly great city, three days' journey in breadth.
3:4 Jonah began to go into the city, going a day's journey. And he cried, "Yet forty days, and Nin'eveh shall be overthrown!"
3:5 And the people of Nin'eveh believed God; they proclaimed a fast, and put on sackcloth, from the greatest of them to the least of them.
3:6 Then tidings reached the king of Nin'eveh, and he arose from his throne, removed his robe, and covered himself with sackcloth, and sat in ashes.
3:7 And he made proclamation and published through Nin'eveh, "By the decree of the king and his nobles: Let neither man nor beast, herd nor flock, taste anything; let them not feed, or drink water,
3:8 but let man and beast be covered with sackcloth, and let them cry mightily to God; yea, let every one turn from his evil way and from the violence which is in his hands.
3:9 Who knows, God may yet repent and turn from his fierce anger, so that we perish not?"
3:10 When God saw what they did, how they turned from their evil way, God repented of the evil which he had said he would do to them; and he did not do it.

-Jonah 3:1-10 RSV

"...from the greatest of them to the least of them...(v. 5)"

Even the infants believed God, proclaimed a fast, and put on the sackcloth? The passage states the entire city, without exception, believed and repented. If children too young to understand what was happening were included in this -and they were- then this means that they were not excluded from the benefits of their families' faith and repentance. They were saved from destruction because of their parents' acts of faith. Later, as they would grow up, God would require them to exercise faith of their own.

Much as in Baptism.

Fruitful work

For as the rain and the snow come down from heaven, and return not thither but water the earth, making it bring forth and sprout, giving seed to the sower and bread to the eater, so shall my word be that goes forth from my mouth; it shall not return to me empty, but it shall accomplish that which I purpose, and prosper in the thing for which I sent it.

-Isaiah 55:10-11 RSV

God's Word accomplishes what it was sent for, but God shows how much He counts on our cooperation. His Word provides for "the sower" and "the eater", but can not help him who refuses to do what God desires. Thus unwilling to sow or eat can not obtain seed or nourishment.

God provides the means for us to accept salvation and live the new life He offers us. But this new life requires us to cooperate with Him. God generously and patiently offers all we need to live this life successfully, but He can't live it for us. For our own good He counts on us to make good use of His gifts.